Genetic Engineering of Bioenergy Crops toward High Biofuel Production

Abstract

Fossil fuels have been widely used as a major energy source, which represents more than 85% of the total energy consumption for economic and social development around the world (Carroll and Somerville 2009). However, global consumption of fossil fuels and their impact on climate change due to greenhouse gas emissions have inspired the development of renewable and sustainable bioenergy for transportation fuels and industrial chemicals (Himmel et al. 2007; Solomon 2010). Bioenergy is considered as a renewable energy derived from biological sources that can be used for heat, electricity, fuel, and chemical products (Yuan et al. 2008; Himmel and Bayer 2009). Globally, land plants can produce approximately 200 billion tons of biomass per year, 70% of which is hypothesized to derive from plant cell walls, an unprecedented resource for biofuel production (Pauly and Keegstra 2008). Over the past years, the first generation of bioenergy systems, including starchor sugar-based ethanol or plant oil–derived biodiesel, has already made a relatively small but significant contribution to global energy supplies. Technologies for the production of bioethanol from starch and biodiesel from lipid have become matured worldwide (Demirbas 2008; Soccol et al. 2010). However, the limited availability of resources and nonsustainability of food-based bioethanol, as well as their competitions with food supply, have triggered a paradigm shift toward the production of lignocellulosic bioenergy (Campbell et al. 2008). The second generation of biofuels such as the ethanol produced from lignocellulosic biomass has received increasing research and development interest (Goh et al. 2010; Mabee and Saddler 2010). The production of lignocellulosic ethanol involves three major processes: biomass pretreatment, lignocellulose enzymatic digestibility, and sugar fermentation. Biomass recalcitrance, which is CONTENTS